1. Field of the Invention
The present invention relates to an exposure apparatus and a device manufacturing method.
2. Description of the Related Art
Projection exposure apparatuses have been used to project and transfer a pattern on a reticle (mask) onto a wafer via a projection optical system. In recent years, there is an increasing demand for exposure apparatuses that achieve high resolving power, high transfer accuracy, and high throughput. As one method that satisfies this demand for high definition, immersion exposure has attracted attention. In immersion exposure, the numerical aperture (NA) of the projection optical system is increased by using liquid as a medium on the wafer side of the projection optical system. The projection optical system has an NA=n×sin θ where n is a refractive index of the medium. Therefore, the NA can be increased to n by filling the gap (also referred to as a ‘space’) between the projection optical system and the wafer with a medium having a refractive index (n>1) higher than the refractive index of air. Further, the resolving power R of the exposure apparatus determined by the process coefficient k1 and the wavelength λ (R=k1×(λ/NA)) is decreased.
As one immersion exposure method, International Publication No. WO99/49504 proposes a local fill method in which the space between a final surface of a projection optical system and a wafer is locally filled with liquid. In the local fill method, it is important to uniformly apply the liquid in a small space between the final surface of the projection optical system and the wafer. For example, if liquid hits on the final surface (final lens) of the projection optical system and flows around the final surface, bubbles are formed in the liquid. Further, if the wafer is moved at a high speed, the liquid spreads or scatters around, and the amount of liquid is reduced. Consequently, bubbles can be easily formed in the liquid. Since the bubbles diffusely reflect exposure light, the amount of exposure light is reduced, and the throughput is reduced. Moreover, since the bubbles hinder the exposure light from reaching the wafer, transfer accuracy is deteriorated.
Japanese Patent Laid-Open No. 2005-353820 discloses an immersion exposure apparatus in which a second liquid recovery port is provided around a final surface of a projection optical system. This immersion exposure apparatus restrains liquid from spreading out.
Further, International Publication No. WO2005/029559 discloses an immersion exposure apparatus in which a secondary liquid recovery port is provided in an inclined trap surface. The trap surface is inclined relative to the XY plane such as to extend away (upward) from a surface of a substrate as it extends toward the outside of an immersion region. The trap surface is subjected to lyophilic treatment. Since films (e.g., a photoresist, an antireflection film, and a protective film) applied on the surface of the substrate are normally water repellant (liquid repellent), liquid flowing out of the second liquid recovery port is trapped by the trap surface. This immersion exposure apparatus having the above-described configuration further restrains the liquid from spreading out.
As described above, in the immersion exposure apparatuses disclosed in Japanese Patent Laid-Open No. 2005-353820 and International Publication No. WO2005/029559, the second liquid recovery port can restrain the liquid from spreading out. However, when a wafer stage moves at a high speed, an interface of the liquid also moves in the moving direction of the wafer stage, and therefore, air easily enters under the projection optical system. As a result, bubbles are easily formed in the liquid. The formation of the bubbles in the liquid can cause reduction in transfer accuracy as described above.
In the exposure apparatus disclosed in International Publication No. WO2005/029559, it can be expected, depending on the inclination angle of the trap surface, that the trap surface prevents the interface of the liquid from moving downward from the projection optical system. In this case, however, the portion near the recovery port where the interface of the liquid normally lies is inclined, and therefore, the pressure of the liquid is changed with the movement of the interface of the liquid. This change in pressure disturbs the driving control of the stage, and decreases the overlay accuracy of the exposure apparatus. As a result, it is difficult to increase the moving speed of the stage.